In the art of refrigerant handling, them is often a need for purging air and other non-condensibles from refrigerant in the refrigerant handling system. U.S. Pat. No. 5,005,369 discloses a system for recovering refrigerant from refrigeration equipment under service with automatic or manual air purge capabilities. This system has enjoyed great commercial acceptance and success for both R-12 and R-134a refrigerant recovery/recycling units in the automotive air conditioner service market. However, the trend in the market, particularly the automotive service market, is toward single service systems that can handle multiple refrigerants. U.S. Pat. Nos. 5,063,749 and 5,181,391 disclose manual purge systems for multiple-refrigerant handling systems, and U.S. Pat. No. 5,285,647 discloses an automatic purge control for a multiple-refrigerant handling system. See also Manz, "How to Handle Multiple Refrigerants In Recovery and Recycling Equipment," ASHRAE Journal, April 1991, pages 22-30, and Manz, The Challenge of Recycling Refrigerants, Business News Publishing, 1995, Chapter 6.
U.S. application Ser. No. 08/463,709, filed Jun. 5, 1995, discloses a refrigerant handling system that includes a chamber for holding refrigerant, and a refrigerant pump for directing refrigerant into the chamber so that the refrigerant collects in liquid phase at the lower portion of the chamber while air and other non-condensibles collect in vapor phase at the upper portion of the chamber over the refrigerant. Sensors are responsive to temperature of the refrigerant entering the chamber and temperature of the refrigerant collected in the lower portion of the chamber. Partial pressure of non-condensibles in the upper portion of the chamber is determined as a function of a difference between such temperatures, and the non-condensibles are purged from the upper portion of the chamber when such partial pressure reaches a selected threshold.
Although the purge control techniques disclosed in the noted patents, publications and application have enjoyed commercial success, and addressed problems theretofore extant in the art, further improvements remain desirable. In particular, there is a need in the art for an automatic purge control technique for use in refrigerant handling systems, particularly refrigerant recovery systems, that is inexpensive, that is intended and adapted for use in conjunction with multiple differing types of refrigerants having differing pressure/temperature characteristics, and that can be readily incorporated into refrigerant handling systems at the time of manufacture or retrofitted to systems in the field. It is a general object of the present invention to provide a refrigerant handling system and method that address these needs in the art.
A refrigerant handling system in accordance with the present invention includes a closed chamber having an inlet for directing refrigerant in liquid phase into the chamber such that the refrigerant collects at a lower portion of the chamber and non-condensibles are trapped in the upper portion of the chamber over the refrigerant. The rate of increase in level of refrigerant in the chamber is measured as liquid-phase refrigerant is directed thereto, and non-condensibles are purged from the upper portion of the chamber when the rate of increase of refrigerant level is less than a preselected threshold. Briefly stated, the present invention operates on the principle that air and other non-condensibles that must be purged from the refrigerant are relatively incompressible as compared with refrigerant vapor. Thus, when refrigerant in liquid phase is fed into the closed chamber, the rate of increase of refrigerant level within the chamber is determined in part by the back-pressure of non-condensibles trapped within the upper portion of the chamber. When such back-pressure of non-condensibles is such that the rate of flow of refrigerant into the chamber, and the corresponding rate of refrigerant level increase within the chamber, is less than a predetermined threshold, the non-condensibles may be purged or vented from the upper portion of the chamber.
In the preferred embodiment of the invention, first and second liquid refrigerant level sensors are coupled to the chamber and responsive to level of refrigerant for providing associated electronic level signals. These level signals are directed to a controller, which functions to measure the time required for the refrigerant level to vary between the levels associated with the respective sensors. When such time is greater than an associated threshold time, the upper portion of the chamber is vented to atmosphere through a flow control orifice. Most preferably, first and second venting orifices are provided, and the controller is operative to vent the upper portion of the chamber through the first orifice when the time required for the change in liquid refrigerant level is greater than a first threshold, and to vent the upper portion of the chamber through the second orifice larger than the first orifice when such time is greater than a second threshold greater than the first threshold. A pressure sensor at the chamber inlet in the preferred embodiment of the invention prevents overloading of any pump or compressor that feeds the chamber by opening the inlet and outlet valves as required to provide a low-pressure refrigerant flow path through the chamber.